Astronomers have discovered a vast, extragalactic void they
call the Dipole Repeller, that appears to be pushing our Local G
The Milky Way galaxy is currently racing through
space at about 2 million km/h (1.2 million mph), on a journey
towards a gravitational anomaly known as the Great Attractor,
which is in turn being dragged towards an even bigger structure,
the Shapley Supercluster. But there's more to the story than
these mysterious monsters: Astronomers have now discovered a
huge extragalactic void, called the Dipole Repeller, that's
pushing us away.
The area of space where these attractors lie is hard
to observe from our vantage point here on Earth. Our Solar
System sits in one of the outer spiral arms of the Milky Way, on
the opposite side to the Great Attractor and Shapley
Supercluster. That means that when we're looking in that
direction, we first have to peer through the stars and dust of
our home galaxy, and in doing so last year, an international
team of researchers discovered over
800 new galaxies in that part of the sky.
The Shapley Supercluster, some 650 million
light-years away, is dense with mass and is constantly drawing
more mass into it, including the entire
Laniakea Supercluster of galaxies that contains the Milky
Way. But the pulling of matter towards concentrated areas is
only part of the equation. Scientists have previously proposed
that a low density region might be pushing matter away at the
same time, but until now, it hadn't been found.
Since it's difficult to observe an absence of
galaxies, a team of researchers from the Hebrew University of
Jerusalem, along with scientists in the US and France, created a
3D map of the "galaxy flow field" – essentially, tracking the
paths that galaxies are taking on their journey through the
universe. Building this map using data from telescopes like
Hubble, the team focused on galaxies with peculiar velocities,
which means they're moving faster than the universe is
expanding. Through statistical analysis of several different
datasets, the team was able to infer the underlying distribution
of mass throughout the universe. The model is made up of
under-dense regions of dark matter that repel mass, and
over-dense regions of luminous galaxies that attract it.
Researchers identified the Dipole Repeller by
creating a 3D map of galaxy flows that represents an area of
space measuring 1.7 billion light years across(Credit:
Daniel Pomarède/ Hebrew University of Jerusalem)
Using this model, the researchers were able to
identify what they call the Dipole Repeller, a large region of
space that's mostly devoid of galaxies, which is repelling our
galactic Local Group.
"By 3D-mapping the flow of galaxies through space,
we found that our Milky Way galaxy is speeding away from a
large, previously unidentified region of low density," says
Yehuda Hoffman, lead researcher on the study. "Because it repels
rather than attracts, we call this region the Dipole Repeller.
In addition to being pulled towards the known Shapley
Concentration, we are also being pushed away from the newly
discovered Dipole Repeller. Thus it has become apparent that
push and pull are of comparable importance at our location."
The Dipole Repeller isn't completely empty, but it
has a relatively low number of galaxies. In the future, the
researchers say that these galaxies could be studied and
properly identified in optical, near-infrared and radio
wavelengths.
The research was published in the journal
Nature Astronomy.
The team describes the Dipole Repeller in the video
below.